1. Field of the Invention
This invention relates to stents and a method for making a stent and delivery system.
2. Description of the Prior Art
It is desirable in various situations to provide means for expanding a constricted vessel or for maintaining an open passageway through a vessel. Such situations arise, for instance, after an angioplasty of a coronary artery. In these situations, wire stents are useful to prevent restenosis of the dilated vessel, or to eliminate the danger of occlusion caused by "flaps" resulting from intimal tears associated with angioplasty. Wire stents can also be used to reinforce collapsing structures in the respiratory and biliary tracts.
Typical of the wire stents of the prior art is the stent of Gianturco, U.S. Pat. No. 4,580,568, wherein the stent is compressed and encased in a sheath. The sheath is then positioned in the vascular system and the stent is held in position by a flat-ended pusher while the sheath is withdrawn. The zig-zag configuration of this particular stent allows it to expand in the passageway to hold the passageway open and enlarged.
Stents comprised of variously shaped spiral springs are described by Maass et al. in U.S. Pat. No. 4,553,545, and in Radiology Follow-up of Transluminally Inserted Vascular Endoprosthesis: An Experimental Study Using Expanding Spirals, Radiology, September 1984; 152:659-663. Application of torque to the end of these spiral springs increases the number of coils while decreasing the stent diameter for insertion. Once inserted, an opposite torque is applied to the spiral springs causing the stent diameter to increase. Use of this type of stent requires a sophisticated coaxial cable to apply torque to the stent once it has been inserted into the vessel.
Dotter et al. reported the use of a prosthesis constructed of a thermal shape memory alloy which is passed into the passageway through a catheter. See, Dotter CT et al., Transluminal Expandable Nitinol Coil Stent Grafting: Preliminary Report, Radiology, April, 1983; 147:259-260. This coil stent is compacted by cooling, inserted, and then heated in situ until the stent expands in the passageway. This stent is positioned within the vessel by a detachable positioning device capable of supplying electrical energy to heat the thermal coil.
Other references which may have relevance to the present invention are the following U.S. patents: Abolins, U.S. Pat. No. 3,278,176; Alfidi et al., U.S. Pat. No. 3,868,956; Simon, U.S. Pat. No. 4,425,908; and Sakura, Jr., U.S. Pat. No. 4,214,587.
Among the drawbacks of the prior art wire stents and expandable coil stents are that these stents are either difficult to produce or complicated to insert into a body passageway. Each of these stents requires the use of a complex device for insertion and expansion of the stent within the vessel. On the other hand, less complex wire stents lack the axial compliance to pass through a catheter that has any significant curves or bends. The present invention addresses each of these problems by providing a wire stent that is easy to produce, simple to install and capable of delivery around curves and bends in a vessel or passageway.